The purpose of this study is to determine the role and value of Spect Thallium imaging in conjunction with a reinjection technique and quantitative analysis to evaluate Viability of myocardium in patients with known CAD. This will be important in determining who will respond best to intervention as well as planning the exact type of intervention based on the results. Patients will have standard Spect Thallium studies after treadmill exercise, but, in addition, a second injection of the tracer will be given at the conclusion of the standard test. A third set of images will be performed approximately 30 minutes later. The reinjection images will be compared to the standard Spect Thallium images to determine if there is any additional advantage to this second injection.